Photocatalysts such as titanium oxide have recently been extensively utilized. Various harmful substances can be decomposed through the utilization of the activity of the photocatalyst excited by photoenergy. Further, the surface of members with a photocatalyst particle-containing surface layer formed thereon can be hydrophilified to allow foulings deposited on the surface to be easily washed away with water. In photocatalyst-containing coating compositions, silicone resins that are less likely to be influenced by oxidative decomposition induced by photocatalysts have been used as suitable binders.
For example, JP H09-227829A (PTL 1) discloses a coating composition including photocatalyst particles, silicone, and an alcoholic solvent. JP 2004-51644A (PTL 2) discloses a coating composition that utilizes an aqueous silicone emulsion from the viewpoint of reducing environmental burden.
Coating films formed by using these coating compositions are relatively hard. For example, when the base undergoes deformation due to exposure to external force or temperature change, in some cases, the coating films cannot be conformed to the deformation of the base, resulting in separation of the coating films or cracking in the coating films. Therefore, a resin emulsion obtained by compositing a polymerizable monomer such as an unsaturated double bond-containing organic compound with a silane compound has been proposed as a binder to form coating films having enhanced base conformability and improved cracking resistance. For example, JP 2008-38113A (PTL 3) discloses a silicone-modified resin emulsion obtained by emulsion-polymerizing an ethylenically unsaturated monomer and an alkoxysilane containing a functional group copolymerizable with the monomer in the presence of a reactive emulsifier. JP 2008-95069A (PTL 4) and JP 2010-106266A (PTL 5) disclose a water dispersion of a composite resin with acid group-containing polymer segments and polysiloxane segments bound to each other.